The Third Generation Partnership Project (3GPP) is developing a new system called an Evolved Packet System (EPS) as a Long Term Evolution (LTE) program. The EPS can achieve improvement of spectral efficiency, shortening of latency and improvement of radio resources, for example. The LTE is the latest standard for a mobile network technique that realizes a GSM (Global System for Mobile communications)/EDGE (Enhanced Data GSM Environment) network technique and a UMTS (Universal Mobile Telecommunications System)/HSPA (High-Speed downlink/uplink Packet Access) network technique. The EPS allows a user to experience a higher data rate and a lot of applications and services at a low cost. In order to make sure a connection to the EPS, a user is required to use a LTE compliant user terminal (User Equipment (UE)).
In the EPS, there are two types of domains including a packet switched (PS) domain and a circuit switched (CS) domain. The PS domain is mainly used for data communications, and satisfies a condition for a higher data rate required by a user. On the other hand, the CS domain is mainly used for voice communications and is widely arranged over a large number of mobile operators so as to enable users to talk to each other.
As a feature of the LTE to implement a smooth shift to the PS domain system, CS fallback (CSFB) is known. This CSFB has a mechanism to allow a network to shift a UE having a CS service function from an access network where a PS domain only exists (e.g., E-UTRAN (Evolved UMTS Terrestrial Radio Access Network) to a CS-compatible access network having a function as a CS domain as well (e.g., UTRAN (UMTS Terrestrial Radio Access Network) for access to a CS service. The CSFB of the EPS allows a UE connected to a PS domain only to receive a voice service by reusing infrastructure already arranged for CS. The CSFB enables a UE to receive a voice call or originate a voice call.
Procedure by a UE or a network to implement the CSFB is described in the following Non-Patent Document 1, for example. For instance, when the network finds the arrival of an incoming CS call addressed to a UE connected to a PS domain only, the network informs the UE to switch (switchover) to a CS domain existing in the neighbor of the UE. As a result of this switchover, the UE is able to receive the incoming CS call. When the UE wants to accept the CS call, the UE connects to the CS domain designated by the network to accept the connection. On the other hand, when the UE does not want to accept the CS call, the UE informs the network to refuse the CS call.
In the case of a UE having a PS session in the PS domain, if the target access network (access network after switchover) supports a PS session as well and approves the connection of the PS session, the network can start a handover of the PS session. When the UE does not decide to return to the original network (access network before switchover) at the end of the CS call, the UE will remain in the target access network. When there is no active session, the UE enters an idle mode, and a determination is made whether the UE should return to the original access network or not in accordance with logic in the UE (e.g., reselection of a cell).
The LTE has another function of introduction of a local IP access (Local Internet Protocol Access: LIPA). The LIPA enables a communication between a UE and a device on a local network without performing a communication passing through a core network of the operator. A local gateway (LGW) is disposed in or in the vicinity of a local network such as a residential or corporate network, and functions as a packet data anchor to the residential or cooperate network. For instance, a user tries to access a device in a residential or corporate network (e.g., when the UE of the user tries to connect to a base station directly connected to a residential or corporate network to access a media server), traffic directly routed between the base station and the residential or corporate network can be as a communication by the LIPA. Thereby, this communication can realize better quality and low cost without using a core network resource of the cellular operator. The LIPA is described in the following Non-Patent Document 2, for example.
The LTE has still another function of selective IP traffic offloading (SIPTO). The SIPTO lets a cellular operator provide a packet data network gateway (PDN GW) near the location of the UE, thus enabling optimization of the traffic path of the UE. For instance, when the UE moves in the network of the cellular operator, policy in the network can detect the allocation of a nearer PDN GW to the UE on the basis of a geographical position or a logical position of the UE. The SIPTO is started by offloading the UE traffic path to a nearer PDN GW without a user's operation. The SIPTO assumes the application to a case of a residual or corporate network as well. Due to the SIPTO, the cellular operator can reduce the usage of a resource in the operator core network, and further a more direct Internet path can be provided to the UE rather than the passage through the operator core network. The SIPTO is described in Non-Patent Document 2, for example.
FIG. 1 shows an exemplary network system relating to the conventional technique and embodiments of the present invention. FIG. 1 exemplifies a system described in the 3GPP. Assume that, in this system, a UE 100 is registered with an operator so as to receive both of a PS service and a CS service. Assume further that the UE 100 exists in the range where an E-UTRAN 101 and a UTRAN 102 overlap. Assume further that the E-UTRAN 101 is a pure PS domain and the UTRAN 102 supports both of a PS domain and a CS domain. The UE 100 currently connects to the E-UTRAN 101, and is located in a user's residential or cooperate network 103. A home E-UTRAN node B (HeNB 104) provides a radio access channel of the E-UTRAN 101 to the UE 100. In order to control an access method of the UE 100 to a service provided by the cellular operator, a Mobility Management Entity (MME 105) executes an access control and authentication procedure required for the UE 100. When the UE 100 is authenticated and authorized for a service provided by the cellular operator, the MME 105 informs the HeNB 104 to provide a necessary resource (via link 106) and establishes a radio connection (i.e., a radio channel) to the UE 100.
When the UE 100 is authorized to receive a data service (e.g., web browsing) via an Evolved Packet Core (EPC) 107 of the cellular operator, the MME 105 selects an appropriate Packet Data Network Gateway (PDN GW 108) to let the UE 100 access the data service. The MME 105 selects an appropriate Serving Gateway (SGW 109) as well to let the UE 100 access the data service. The MME 105 requests the SGW 109 to set up a necessary connection (link 111) to the PDN GW 108 relating to the UE 100. The MME 105 further requests the SGW 109 to set up a necessary EPS bearer (link 112) to the HeNB 104 relating to the UE 100. When a data path relating to the UE 100 is set up, the application (e.g., a web browser) of the UE 100 can access the Internet 113 or other networks via the PDN GW 108. The PDN GW 108 uses a link 114 to transfer a data packet from/to the UE 100 to/from the Internet 113 or other networks.
The following considers the case where the UE 100 can use the LIPA and the UE 100 tries to download a certain file (e.g., a data file or a video file) from a server (hereinafter called a media server 115) located in a home network 118. In order to allow the UE 100 to perform a communication to the residential or cooperate network 103, a Local Gateway (LGW 116) connected to the residential or cooperate network 103 has to be allocated to the UE 100. The UE 100 sends a request to the MME 105 to require a connection to the residential or cooperate network 103. The UE 100 informs the MME 105 that the request is for a connection to the residential or cooperate network 103. Considering subscriber information on the UE 100, the MME 105 searches for an appropriate PDN GW for the UE 100. Through this searching procedure, the MME 105 decides to allocate the LGW 116 to the UE 100 for the LIPA in the residential or cooperate network 103. The MME 105 requests the LGW 116 to set up an EPS bearer (link 117) necessary for the UE 100 and inform the MME 105 that the EPS bearer is set up.
Herein, the LGW 116 and the HeNB 104 can communicate with each other (via link 119). For instance, when the LGW 116 has a data packet relating to the UE 100, the data packet is transmitted via the link 119. When the UE 100 leaves the residential or cooperate network 103, the LGW 116 communicates with the SGW 109 (via link 120) and can support a remote access to the residential or cooperate network 103. The remote access to the residential or cooperate network 103 is permitted on the basis of a user's subscriber profile.
When the MME 105 is informed that the EPS bearer is set up, the MME 105 requests the HeNB 104 to set up a radio bearer necessary for the UE 100. Herein, the MME 105 passes an identifier of the EPS bearer to the HeNB 104, whereby the HeNB 104 can create mapping of the radio bearer of the UE 100 with the EPS bearer. When the radio bearer for the UE 100 is set up, the UE 100 can start a data communication at the residential or cooperate network 103. For instance, the UE 100 can download a data file from the media server 115. In this case, a data path will pass through link 121 where the LGW 116 has a connection with the home network 118. A usual connection to the Internet can be provided to a user in the residential or cooperate network 103, whereby the UE 100 is permitted to access the Internet. For instance, traffic from the Internet 113 reaches the home network 118 via link 122, and subsequently reaches the LGW 116 via the link 121. The LGW 116 transfers the traffic from the Internet 113 to the UE 100. Herein, the above description is one example implemented with one arrangement configuration at the residential or cooperate network 103, and the residential or cooperate network 103 may have a different arrangement configuration.
When receiving, from a Mobile Switching Center (MSC 128), a trigger indicating that an incoming CS call addressed to the UE 100 exists, the MME 105 transmits a CS service notification to the UE 100 to inform that a CS call is pending (pending CS call exists). This trigger is transmitted via link 129. Receiving a response from the UE 100 that the UE 100 receives the incoming CS call, the MME 105 informs the HeNB 104 that the UE 100 has a pending CS call. Receiving the notification about a pending CS call relating to the UE 100, the HeNB 104 searches for an appropriate CS domain to let the UE 100 receive the CS call. Assume herein that the HeNB 104 can estimate that a Base Station Subsystem (BSS) 123 is an appropriate candidate to handle the CS call of the UE 100 using a measurement report from the UE 100, for example. In this case, the HeNB 104 requests the MME 105 to transfer a request to the BSS 123 requesting to prepare for a handover of the UE 100 to the UTRAN 102. The MME 105 finds that the BSS 123 is managed by the MSC 128 and connects to the MSC 128 via the link 129. As described above, it is assumed that the UTRAN 102 cannot support a PS service. Therefore, the MME 105 performs a communication with the MSC 128 to let the UE 100 perform a handover to the UTRAN 102.
The MME 105 passes necessary context (e.g., a security key) to the MSC 128, whereby the MSC 128 can prepare for reception of the incoming CS call of the UE 100. When the MSC 128 finds that the UE 100 is to be handed over to the UTRAN 102, the MSC 128 informs the BSS 123 via link 130 to prepare for a radio resource of the CS call. When the BSS 123 becomes ready for reception of the UE 100, the BSS 123 informs the HeNB 104 to issue an instruction to the UE 100 to switch to the UTRAN 102 (via the MSC 128 and the MME 105). Then, the UE 100 switches to the UTRAN 102 and receives the incoming CS call.
Herein, when the UTRAN 102 supports PS traffic as well, a SGSN (Serving GPRS Support Node) 124 will perform the processing relating to a handover of PS traffic of the UE 100. In this case, the MME 105 passes necessary context (e.g., a security key) to the SGSN 124, whereby the SGSN 124 can prepare for the PS traffic of the UE 100. The MME 105 further informs the SGSN 124 of an EPS bearer identifier. The SGSN 124 creates mapping of the EPS bearer identifier to a corresponding packet data protocol (PDP) context, and passes the EPS bearer identifier to the BSS 123. The SGSN 124 further sets up a connection to any one of the PDN GW 108 and the LGW 116 via the SGW 109 (link 127) for a PS session of the UE 100. For instance, when the UE 100 is permitted to make a remote access to the residential or cooperate network 103, the UE 100 can continue a data connection to the LGW 116 in the UTRAN 102 (via links 126, 127 and 120).
FIG. 2 shows another exemplary network system relating to the conventional technique and embodiments of the present invention. FIG. 2 exemplifies a system described in the 3GPP. In this system, a UE 200 is registered with an operator so as to receive both of a PS service and a CS service. Assume that the UE 200 exists in the range where an E-UTRAN 201 and a UTRAN 202 overlap. Assume further that the E-UTRAN 201 is a pure PS domain and the UTRAN 202 supports both of a PS domain and a CS domain. The UE 200 currently connects to the E-UTRAN 201. In the E-UTRAN 201, an eNB 203 provides a radio access channel in the E-UTRAN 201 to the UE 200. In order to control an access method of the UE 200 to a service provided by the cellular operator, a MME 204 executes an authentication procedure and an access control procedure necessary for the UE 200. When the UE 200 is authenticated and authorized for a service provided by the cellular operator, the MME 204 informs the eNB 203 to provide a necessary resource (link 205) and establishes a radio connection (i.e., a radio channel) to the UE 200.
When the UE 200 is authorized to receive a data service (e.g., video streaming from a media server 208) via an EPC 206 of the cellular operator, the MME 204 selects an appropriate PDN GW (PDN GW 207) to let the UE 200 access the data service. The MME 204 selects an appropriate serving gateway (SGW 209) as well to let the UE 200 access the data service. The MME 204 requests the SGW 209 to set up a necessary connection (link 211) to the PDN GIN 207 for the UE 200. The MME 204 further requests the SGW 209 to set up a necessary EPS bearer (link 212) to the eNB 203 for the UE 200. When a data path relating to the UE 200 is set up, the application (e.g., a media player) of the UE 200 can access the Internet 213 or other networks via the PDN GW 207. The PDN GW 207 uses link 214 to transfer a data packet from/to the UE 200 to/from the Internet 213 or other networks.
When receiving, from a MSC 222, a trigger indicating that an incoming CS call addressed to the UE 200 exists, the MME 204 transmits a CS service notification to the UE 200 to inform that it is a pending CS call. This trigger is transmitted via link 223. Receiving a response from the UE 200 that the UE 200 receives the incoming CS call, the MME 204 informs the eNB 203 that the UE 200 has a pending CS call. Receiving the notification about a pending CS call relating to the UE 200, the eNB 203 searches for an appropriate CS domain to let the UE 200 receive the CS call. Assume herein that the eNB 203 can estimate that a BSS 215 is an appropriate candidate to handle the CS call of the UE 200 using a measurement report from the UE 200, for example. In this case, the eNB 203 requests the MME 204 to transfer a request to the BSS 215 requesting to prepare for a handover of the UE 200 to the UTRAN 202. The MME 204 finds that the BSS 215 is managed by the MSC 222 and connects to the MSC 222 via the link 223. As described above, it is assumed that the UTRAN 202 cannot support a PS service. Therefore, the MME 204 performs a communication with the MSC 222 to let the UE 200 perform a handover to the UTRAN 202.
The MME 204 passes necessary context (e.g., a security key) to the MSC 222, whereby the MSC 222 can prepare for reception of the incoming CS call of the UE 200. When the MSC 222 finds that the UE 200 is to be handed over to the UTRAN 202, the MSC 222 informs the BSS 215 via link 224 to prepare for a radio resource of the CS call. When the BSS 215 becomes ready for reception of the UE 200, the BSS 215 informs the eNB 203 to issue an instruction to the UE 200 to switch to the UTRAN 202 (via the MSC 222 and the MME 204). Then, the UE 200 switches to the UTRAN 202 and receives the incoming CS call.
Herein, when the UTRAN 202 supports PS traffic as well, a SGSN 216 will perform the processing relating to a handover of PS traffic of the UE 200. In this case, the MME 204 passes necessary context (e.g., a security key) to the SGSN 216, whereby the SGSN 216 can prepare for the PS traffic of the UE 200. The MME 204 further informs the SGSN 216 of an EPS bearer identifier. The SGSN 216 creates mapping of the EPS bearer identifier to a corresponding PDP context, and passes the EPS bearer identifier to the BSS 215. The SGSN 216 further sets up a connection to the PDN GW 207 via the SGW 209 (link 219) for a PS session of the UE 200. Thereby, the UE 200 can continue a data connection to the PDN GW 207 in the UTRAN 202 (via links 218, 219 and 211).
Assume herein that the SGSN 216 decides to offload the data connection between the UE 200 and the PDN GW 207 to a GGSN (Gateway GPRS Support Node) 220, thus executing SIPTO for this data connection. In this case, data traffic of the UE 200 will be managed by the GGSN 220. Herein, the reason for the SGSN 216 triggering the SIPTO is that the policy of the SGSN 216 detects that the link 219 is not efficient for routing of the data traffic of the UE 200 and consumes a large quantity of network resources, for example. Another reason is that the link 219 is in a congestion state and cannot support the data traffic of the UE 200, for example.
For instance, assume that the application (e.g., a video player) of the UE 200 originally performs streaming of video from the media server 208 disposed in the Internet 213 via the PDN GW 207 (links 212, 211 and 214). When the UE 200 performs a handover from the E-UTRAN 201 to the UTRAN 202, the video stream of the UE 200 will be transmitted through the links 218, 219, 211 and 214. Herein, the SGSN 216 detects that the data traffic of the UE 200 is not transferred along an optimum path, and decides to offload, to the GGSN 220, the data connection of the UE 200 to the PDN GW 207. The SGSN 216 requests the UE 200 to disconnect the data connection of the UE 200 to the PDN GW 207 and transmit a request for a data connection. Then, the UE 200 transmits the request and the SGSN 216 selects the GGSN 220 as a data gateway of the UE 200. As a result, the video player of the UE 200 receives a video stream from the media server 208 via the GGSN 220 (links 218, 221 and 222). Herein, the IP address of the UE 200 may change during the offload procedure, and in this case, the progressing session of the UE 200 to the media server 208 may not continue.
Patent Document 1 discloses a method of making a user define a policy set to decide how to handle CSFB. In Patent Document 1, a user configures a policy, as a policy that can be configured inside a UE, for example, such that when there is a currently progressing important PS session, the UE ignores a page relating to CSFB from a network. In another embodiment disclosed, a UE inserts a flag informing a MME that CSFB should not interfere with the current session during a service request procedure.
Patent Document 2 discloses the following technique. When a MME receives an instruction to hand over a UE to a network of another access technique, the MME informs the UE that a PS session of the UE is interrupted, and as a result the UE can resume the data session at a target access network when the UE connects to the target access technique.
Patent Document 3 discloses a method for reselection of a better RAT (Remote Access Technology) that can support voice services. According to the method, a voice application of a UE changes the priority of frequency/RAT in a priority list.